Electrical connectors (hereinafter, simply called a connector) that interconnect printed wiring boards (hereinafter, simply called wiring boards), having electronic components mounted in a parallel, are commonly known in the art, especially when used inside electronic equipment such as the personal computer. These connectors are generally mounted on each of the wiring boards, and are sometimes known as vertical headers.
Japanese Utility Model Laid-Open No. 4-99378 discloses a high-density connector, which is a compact connecter having a number of contact members. As shown in FIG. 14, the connector 200 has a plurality of terminal plate mating portions 202 formed in the rear portion of a housing 201, and after terminal units 203 mate with the terminal plate mating portions 202, each of the terminal units 203 are then welded to the housing 201, rigidly connecting the two. In the terminal unit 203, a number of contact members 205 and 206 are embedded in a terminal plate 204. The terminal plate 204 being short in dimension along a longitudinal direction with a narrow width in two rows at predetermined pitches. Contact portions 205a and 206a of the contact members 205 and 206 are disposed in a mating recess 207, along insulated walls 208 formed in the mating recess 207 of the housing 201.
In the connector 200, projections 208a are formed at upper end portions of the insulated walls 208. In plan view, the contact portions 205a and 206a are hidden by the projections 208a. Specifically, the projections 208a are provided to prevent the contact members of a mating connector (not shown) from colliding with the tip ends of the contact portions 205a and 206a when the connector 200 mates with the mating connector. When the contact members of the mating connector collide with the tip ends of the contact portions 205a and 206a, mating may become insufficient. Alternatively, the contact portions 205a and 206a and even the contact members of the mating connector may be damaged.
With the miniaturization of electrical equipment, the connector 200 is required to be of a reduced height, that is, to reduce its height in correspondence with size of electronic equipment. However, it is not advantageous to minimize the height of the connector 200, in which the projections 208a are provided at the tip ends of the insulated walls 208, because the insulated walls 208 become higher correspondingly to formation of the projections 208a. 
As shown in FIG. 15, a connector 300 described in Japanese Patent Laid-Open No. 2001-102120 is not provided with the projections at the upper ends of the insulated walls, as described in the Japanese Utility Model Laid-Open No. 4-99378 connector 200, and therefore, the connector 300 can be reduced in height.
Incidentally, a contact member 303 is only restrained to a housing 301 by press-fitting its raised portion into a bottom floor 301b. Accordingly, when a force is applied to a tine portion 303b of the contact member 303 in the direction shown by an arrow, the contact member 303 rotates in the direction shown by an arrow around the press-fitted portion. Thereupon, a contact portion 303a displaces in the direction away from an insulated wall 302. Thereupon, the contact portion 303a is likely to collide with a contact portion 304a of a contact member 304 of a mating connector. Hereinafter, displacement of the contact portion 303a in the direction to be away from the insulated wall 302 will be called “lift” of the contact portion.
When the thickness of the bottom floor 301b of the housing 301 becomes thin, the contact member 303 may easily rotate when a force is applied to the tine portion 303b in the direction shown by the arrow. This is because the length of the bottom floor 301b, which restrains the contact member 303, becomes short. When the connector 300 is reduced in height, a predetermined mating length needs to be measured. Therefore, the thickness of the bottom floor 301b is made thin. Accordingly, when the connector 300 is reduced in height, the contact portion 303a is easily lifted from the insulated wall 302.